MEMS is a micro electromechanical system which integrates a micro sensor, an executer and a signal processing and controlling circuit, an interface circuit, communication and a power supply as a whole. In recent years, the traditional mechanical sensor is progressively replaced by the MEMS pressure sensor in the fields of automotive electronics, consumer electronics and industry electronics, and the MEMS pressure sensor has broad market prospects. For example, the MEMS technology is widely used in a tire pressure monitoring pressure sensor, an engine oil pressure sensor, an automotive braking system air pressure sensor, an automotive engine intake manifold pressure sensor and the like.
As compared to the traditional mechanical sensor, the MEMS pressure sensor has a smaller size, a higher control precision and a manufacturing process compatible with the silicon IC technology; and therefore, the performance/cost ratio of the MEMS pressure sensor is greatly improved. At present, the MEMS pressure sensor includes piezoresistive type pressure sensor and capacitive type pressure sensor, either of which is a MEMS sensor manufactured on a silicon chip. The piezoresistive pressure sensor applies the principle of a resistance of a silicon resistor changing under a stress (a pressure) and adopts a Wheatstone bridge consisting of a high-precision silicon resistance strain gauge as a force-electricity conversion measuring circuit, high measuring precision and a lower power consumption may be obtained.
The traditional manufacturing method for the piezoresistive pressure sensor includes: firstly, forming multiple resistors or a Wheatstone bridge on a silicon substrate by using an ion implantation or a diffusion process; then forming a sensitive diaphragm by etching an area of the silicon substrate where the resistors are located through a wet-etching or dry-etching process; and finally forming a pressure reference cavity at the backside of the sensitive diaphragm through a sealing process, and performing a packaging process to form a chip of a sensor. The sensitive diaphragm generates a deformation or a stress under an external pressure, and a change in the resistance of the resistor or the Wheatstone bridge is generated correspondingly. Under a voltage basis, the change in the resistance described above is converted to a voltage signal which is taken as an output signal after being amplified by a signal processing circuit. The main processes of this manufacturing method are similar to that of a CMOS integrated circuit.
Recently, Bosch has invented a manufacturing method for a piezoresistive pressure sensor. The method adopts a special process to form a buried cavity in a certain area of a silicon substrate, and thus does not use the traditional deep silicon etching process to form a sensitive diaphragm. STMicroelectronics manufactures a cavity in a monocrystalline silicon substrate by processes of etching, epitaxy and annealing to form a monocrystalline silicon surface film and the piezoresistive pressure sensor.
After a traditional MEMS pressure sensor has been manufactured, a packaging process with a signal processing chip will be performed: a pressure sensor chip and a signal processing circuit chip are disposed on a packaging cavity substrate and are coupled to each other through wire-bonding; then the chips are coated with a protective soft gel and finally sealed with a plastic cover or a metal cover. Furthermore, the pressure sensor chip and the signal processing circuit chip may firstly disposed on the planar packaging substrate and the chips are coupled through wire-bonding; and then the chips are coated by a protective soft gel and covered by a metal housing.
However, the problem is that, in the above manufacturing and packaging method for the traditional MEMS pressure sensor, the pressure sensor chip and the signal processing circuit chip are discrete chips and integrated together by a packaging process. The process for the cavity packaging with the plastic cover or a metal cover is complicated and thus not easily compatible with the mature integrated circuit (IC) manufacturing technology, leading to a higher cost and a larger size.